Changing the shape and color of hair represents an important area of modern cosmetics. In addition to coloring, the lightening of the natural hair color, or hair bleaching, is a very specific desire of many consumers since a blonde hair color is regarded as attractive and desirable in terms of fashion. A variety of hair-bleaching agents, with differing hair-bleaching performance, are available on the market for this purpose.
The oxidizing agents included in hair-bleaching agents are capable of lightening hair fibers by oxidative destruction of the hair's own melanin dye. For a moderate hair-bleaching effect it is sufficient to use hydrogen peroxide—optionally with the use of ammonia or other alkalizing agents—as the only oxidizing agent; to achieve a stronger hair-bleaching effect it is usual to use a mixture of hydrogen peroxide and peroxodisulfate salts and/or peroxomonosulfate salts.
For stability reasons, commercially available hair-bleaching agents are usually offered in two preparations packaged separately from one another, which are mixed together immediately before use to provide a completed preparation for use. Commercially available hair-bleaching agents usually consist of a liquid oxidizing agent preparation and a powder that includes solid oxidizing agents.
For hair bleaching, the powder that includes the solid oxidizing agents is mixed with the hydrogen peroxide solution immediately before use. This mixture is then applied to the hair and is rinsed out again after a contact time. In order to attain a sufficient hair-bleaching effect, agents of this type are usually made heavily alkaline; the pH value here lies between 9 and 10.5. High pH values of this kind are necessary to ensure an opening of the outer cuticle layer (cuticula) and thus enable a penetration of the active species (hydrogen peroxide and persulfates) into the hair.
In the case of human hair, trace elements such as copper, iron and zinc can become concentrated. Heavily bleached hair or damaged hair demonstrates an increased affinity to absorb trace elements.
The accumulation of metal ions in the hair fibers can also be caused by drinking water. In some southern European countries and also in some regions of the USA, water that includes high quantities of metal ions is used for daily bodily hygiene. Certain living conditions, however, such as the necessary administration of drugs such as cisplatin in the case of cancer therapy, increase the metal content in the body. The medical prescription of iron preparations to be taken during pregnancy or in the case of heavy menstrual bleeding as well as zinc preparations as agents to help combat dermatitis is routine practice. The daily administration of dietary supplements based on mineral substances forms part of a healthy lifestyle for some people.
These factors are potential sources that could lead to an accumulation of trace elements/metal ions above the necessary essential level in the body and ultimately in hair.
The metal ions concentrated in the hair fibers can catalyze the decomposition of the hydrogen and persulfates, which leads to an undesirable development of heat.
U.S. Pat. No. 5,635,167 thus proposes a method for removing metal ions such as copper or iron, in which a solution that includes 4 to 25 wt. % of a chelating agent and having a pH value from 4 to 9 is used.
EP 1714634 A1 describes hair-treatment kits for coloring human hair, comprising a first compartment, which includes a complexing agent, and a second compartment, which includes coloring agents. Here as well, undesirable reactions on and with hair that lead to an undesirable heating are prevented.
It has been found, however, that an undesirably high development of heat can still occur also in hair-bleaching agents that include complexing agents.
There is still a need to provide hair-bleaching agents which, when used, reduce the development of heat and the resultant damage to hair and/or the scalp.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.